Embroyology

Question 1

Describe the formation of the retina (Include of the germ layers it derives from, where the blood supply comes from)

Answer 1

Week 4: Optic pits form on the neural tube, grow into optic vesicles connected to the neural tube by the optic stalks.
-the optic vesicles grow forwards towards the surface ectoderm.
-When it makes contact with the surface ectoderm the surface ectoderm thickens ( this will become the lens)
-When the surfaces thicken they become the lens placode.
-These surfaces then inviaginate together.
-The invaginated surface ectoderm separates and becomes the lens vesicle and the
invaginated optic vesicle is now the optic cup.
-At week 6 this becomes the retina and
ganglion cells start to form.
-At 20 weeks the macula forms.
-The retina develops from the outer walls of the optic cup.
The outer, thinner layer of the optic cup becomes the retinal pigment epithelium, whereas the inner thicker layer differentiates into the neural retina. The two retinal layers are separated by an intraretinal space,

The inner layer of the optic cup proliferates to form a thick neuroepithelium. Also the cells of the inner layer, differentiate into the neural
retina (the photsensitive region).
the neural retina is inverted (ie light sensitive parts of the neural retina are adjacent to the retinal pigment epithelium. The cavity of the optic stalk is gradually filled with axons forming the optic nerve

The developing eye is initially supplied with blood by the hyaloid artery. This becomes the central retinal vein and artery

Question 2

What is the purpose of the hyaloid artery? When does it develop and what happens to it?

Answer 2

To nourish the developing lens with a blood supply. Some becomes the central retinal artery,
some does not exist in the developed eye, it is only present during embryological
development

Question 3

Which eye components develop from the neural ectoderm?

Answer 3

Optic nerve, retina

Question 4

Which eye components develop from the surface ectoderm?

Answer 4

Corneal epithelium, lens, eyelid and glands, conjunctiva and lacrimal drainage

Question 5

When do the eyes start to develop

Answer 5

Week 4

Question 6

Fertilisation

Answer 6

a complex sequence of co-ordinated molecular events that begins with contact between a perm and an oocyte and ends in the intermingling of maternal and paternal chromosomes at metaphase of the first mitotic division of the zygote

Question 7

Meiosis

Answer 7

The process in which the sperm and egg reduce their chromosome sets down to 1

Question 8

What is gametogenesis?

Answer 8

The formation of gametes that are then able to combine during fertilisation

Question 9

What is a zygote?

Answer 9

Formed when one gamete from each parent combine to form a single cell

Question 10

What occurs during mitosis?

Answer 10

The cell nucleus divides with the same chromosomal information to form a new cell

Question 11

What are blastomeres?

Answer 11

The zygote becomes a blastomere when mitosis has occurred

Question 12

What is a morula?

Answer 12

A blastomere becomes a morula once cleavage has occurred, containing 16 cells that move to the fallopian tube

Question 13

Define cleavage in the context of embryonic development.

Answer 13

Repeated mitotic divisions

Question 14

When does blastocyst formation occur?

Answer 14

At day 4, when mitosis continues and the cells reorganise to form an outer and inner cell layer

Question 15

What is the trophoblast?

Answer 15

The layer of cells that becomes the placenta

Question 16

What does the embryoblast become?

Answer 16

The embryo

Question 17

What is an ectopic pregnancy?

Answer 17

When the blastocyst implants outside of the womb

Question 18

Define differentiation.

Answer 18

When a cell changes from one type to another, usually a more specialized type of cell

Question 19

What structures does the ectoderm give rise to?

Answer 19

• Epidermis
• Nervous system
• Retina
• Various other structures

Question 20

What does the endoderm develop into?

Answer 20

The source of epithelial linings of the respiratory and digestive tract, including glands

Question 21

What does the mesoderm give rise to?

Answer 21

• Smooth muscular coats
• Connective tissues
• Vessels associated with tissues and organs
• Most of the cardiovascular system
• Blood cells
• Bone marrow
• Skeleton
• Striated muscles
• Reproductive and excretory organs

Question 22

What is the notochord?

Answer 22

The first structure to develop from the mesoderm, which is the basis for the head and spinal cord

Question 23

What is neurulation?

Answer 23

The processes involved in the formation of the neural plate and neural folds, and the closure of these folds to form the neural tube

Question 24

What does invagination refer to?

Answer 24

A structure folding in on itself (e.g., of the optic cup)

Question 25

Week 1

Answer 25

• Fertilisation • Zygote formation • Meiosis • Formation of blastocyst • Implantation into the womb

Question 26

What is happening in week 2

Answer 26

• Blastocyst attaches to endometrial epithelium • Uteroplacental circulation established • Rapid proliferation and differentiation of blastocyst (trophoblast) • Embryo forms • Amniotic cavity develops

Question 27

What is happening in week 3

Answer 27

-Primitive streak develops • Proliferation and migration of cells • Ectoderm cells move towards cranial end of embryo

Question 28

What is happening in week 4

Answer 28

• Eyes and ears start to grow • Heart is beating • Neural tube is separate • The ectoderm separates into the Neural Ectoderm and the Surface ectoderm

Question 29

What is happening in week 5

Answer 29

• Optic cup becomes the retina • Optic stalk becomes the optic nerve • The outer rim of the optic cup contributes to the epithelial layers of the iris ciliary muscles and iris muscles

Question 30

What is happening in week 6

Answer 30

Ganglion cells form in the retina